The Toxic Pitohui Birds

Here's an advisory to the uninitiated or would-be birders, or simply bird-lovers, especially those traveling to some of the world's least explored countries to pursue their hobby. In Papua New Guinea, a country in the Oceania region, three species of birds - belonging to the genus Pitohui - have been found to conceal a certain toxin in their skins and feathers. When examined by five noted biologists, led by Jack P. Dumbacher of the University of Chicago, the toxin was found to cause burning, numbness, and sneezing in human nasal tissues. For this reason, the natives of that country branded the pitohui birds as "rubbish birds."

These three toxic birds were identified as the hooded pitohui (P. dichrous), rusty pitohui (P. ferrugineus), and variable pitohui (P. kirhocephalus). Of the three, the hooded pitohui is considered the most toxic. Specimens of the birds, including the skin, feathers, striated muscles, and stomach with contents, among others, were collected by Dumbacher and his fellow biologists from the National Institutes of Health in Bethesda, Maryland and the Smithsonian Institution in Washington, D.C.

From the specimens, the toxin was set apart from the other substances. It was then identified and was observed to be a homobatrachotoxin. This poison, a steroidal alkaloid, is much like the one found in the poison-dart frogs (or poison-arrow frogs) that are native to Central and South America, and whose skins the native Colombians use to manufacture poison to be spread on blow-gun darts and arrows.

The toxicity of the poison in the pitohui birds was tested by injecting subcutaneously tissue extracts (from the specimens collected) into the hindquarters of laboratory mice. Depending on the dosage injected, the toxin caused in the mice partial or complete loss of locomotor function, convulsions, and, worst, death. The toxin was found to activate sodium conduits in cells, hindering the increase in the resistance of membranes. The skins and feathers were found to be the most toxic of all tissues tested, while those taken from the hooded pitohui were observed to contain the highest level of toxicity of the three pitohui species.

The biologists concluded that the toxin serves as a defense of the pitohui birds against natural predators, including snakes and some of the tree-dwelling marsupials. This conclusion became the basis of the fact now widely recognized in the ornithological field that the pitohui birds are the first known poisonous members of the class Aves warm-blooded vertebrates. The pitohui birds have two other characteristics: they are brightly colored in contrasting orange-brown and black and they give off a strong, rancid smell. These two factors make the pitohui birds highly unwanted preys to roving predators. [Read the Original Article]

Source: http://www.bbc.co.uk/dna/h2g2/alabaster/A647895